All calls are not recorded or the quality of the recording is very poor or nonexistent, why?

There are 5 possible reasons:

There is another recorder working in your phone that blocks Mobile Tracker Free. Android allows only one recorder working, so you MUST remove ALL other recorders at first, otherwise Mobile Tracker Free will surely fail to record calls.

You are using a "voice assistant" app, the app is occupying the microphone, it's continuously picking up sound from the microphone to recognize your "voice command", and this blocks Mobile Tracker Free working. Please disable the voice assistant app.

The "OK Google" app is the most popular voice assistant in Android phones, please disable the following option in your phone:

In some Huawei phones, maybe it's in a different location, read your user manual if needed.

For other phones it's possible the manufacturer has it's own voice assistant in the phone, please check it.

In rare cases, the program may not record voice calls on some phone models. This is due to their hardware and software features that deviate from Android specifications (Non-exhaustive list: Google Pixel, Nexus 6P, Nexus 6, Nexus 5X, Nexus 5, Nexus 4, Moto G4, HTC M7).

Only normal calls can be recorded, wifi calls can't be recorded no matter, so if your phone supports the wifi call feature please disable it.

If your phone has Android version 9 Pie, the quality of recording will be very low or nonexistent, the solution is to activate the speaker.

Solution:

If the problem persists, you should try changing the configuration type of call and types of audio files from the 'Features Selection'.